[boost] [mpl]suggested addition in vault/cppljevans/mpl/child_i_depth_j.zip

child_i_depth_j allows the traversal of a tree of applications. It's useful for accessing, for example, the i-th superclass of the results of mpl/fold, as demonstrated by the test file: libs/mpl/test/child_i_depth_j_test.cpp included in the zip file mentioned in the subject line. Could this be added to mpl? Is there something I could do to facilitate this addition? -regards Larry